Because of their high volumetric efficiency and thus their small size, multilayer ceramic capacitors (MLC's) are the most widely used form of ceramic capacitors. These capacitors are fabricated by stacking and co-firing thin sheets of ceramic dielectric on which an appropriate electrode pattern is printed. Each patterned layer is offset from the adjoining layers in such manner that the electrode layers are exposed alternately at each end of the assemblage. The exposed edges of the electrode pattern are coated with a conductive material which electrically connects all the layers of the structure, thus forming a group of parallel connected capacitors within the laminated structure. Capacitors of this type are frequently referred to as monolithic capacitors.
The thin layers of ceramic dielectric used for the fabrication of multilayer devices are comprised of a layer of finely divided dielectric particles which are bound together by an organic polymeric material. The unfired ceramic can be prepared by slip casting a slurry of the dielectric particles dispersed in a solution of polymer, plasticizer and solvent onto a carrier such as polypropylene, Mylar.RTM. polyester film or stainless steel and then adjusting the thickness of the cast film by passing the cast slurry under a doctor blade to form a thin "green tape".
Metallizations useful in producing conductors for multilayer structures normally comprise finely divided metal particles applied to green tape in the form of a dispersion of such particles in an inert liquid vehicle. Although the above-described "green tape" process is more widely used, there are nevertheless other procedures with which dielectric compositions of the invention can be used to make such structures. One technique is the so-called "wet process". In one aspect, this may involve passing a flat substrate through a falling sheet of dielectric slip one or more times to build up a dielectric layer (see Hurley et al., U.S. Pat. No. 4,717,487).
Another "wet process" method of making multilayer structures involves forming a paste of the dielectric material and then alternately screen printing the dielectric and metal layers with intervening drying steps until the designed structure is complete. A second electrode layer is then printed atop the dielectric layer(s) and the entire assemblage is cofired.
There is a need for low k dielectrics that can be used in multilayer structures for high frequency applications. These dielectrics must meet the industry COG specification for temperature stability of better than +/-30 ppm/.degree.C. and must have low loss at 1 MHz, e.g. D.F. 0.1%, Q 1000. In addition, dielectrics are required that can be sintered at temperatures low enough to permit use of high silver content electrodes (e.g. 70% Ag-30% Pd) instead of costly palladium. If these dielectrics can also be sintered in atmospheres of low oxygen content, then copper electrodes could be used for even further cost reduction, and possible improved performance.